The Lepidoptera have, over millions of years, evolved a wide range
of wing patterns and colouration ranging from drab moths akin to
the related order Trichoptera to the
brightly coloured and complex-patterned butterflies. Accordingly,
this is the most recognised and popular of insect orders with many
people involved in the observing, study, collecting, rearing and
commerce of these insects. A person who collects or studies this
order is referred to as a lepidopterist. Many species of the order are
of economic interest by virtue of the silk they produce, or being
pests, or due to the pollination they carry out.

The larvae, caterpillars, have a
toughened (sclerotized) head capsule,
chewing mouthparts, and a soft body, that may have hair-like or
other projections, 3 pairs of true legs, and additional prolegs (up to 5 pairs). They can be confused with
the larvae of sawflies. Lepidopteran larvae
can be differentiated by the presence of crochets on the prolegs
which are absent in the Symphyta
(sawflies). Most caterpillars are herbivores, but a few are carnivores (some eat ants or other caterpillars)
and detritivores.

Adults have two pairs of membranous wings covered, usually
completely, by minute scales. In
some species, wings are reduced or absent (often in the female but
not the male). Antennae are prominent. In moths, males frequently
have more feathery antennae than females, for detecting the female
pheromones at a distance. The Trichoptera (caddisflies) which are a sister
group of the Lepidoptera have scales, but also possess caudal cerci
on the abdomen, a feature absent in the
Lepidoptera.[[Image:Butterfly-description.svg|thumb|250px|A labeled
Papilio machaon:A- ForewingB - AntennaC - Compound eyeD - ProboscisE - ThoraxF - LegG- AbdomenH - HindwingI - Tail]]

Adult mouth parts prominently include the
proboscis formed from maxillarygaleae and are
created for sucking nectar. Some species have
reduced mouth parts (some species do not feed as adults), and
others have them modified to pierce and suck blood or fruit juices
(some Noctuids). Mandibles are absent in all except the Zeugaloptera which have chewing mouthparts. The
maxillary palpi are reduced and consist of up to five segments.
They are conspicuous in some of the more primitive families and are
often folded. The labial palpi are more prominent and upward
pointed.(See also: difference between a
butterfly and a moth)

The three thoracic segments are fused and consist of non-movable
sclerites. The wings arise from the meso-
and meta-thoracic segments and are similar in size in the primitive
groups. In the more recent groups, the meso-thoracic wings are
larger with more powerful musculature at their bases and more rigid
vein structures on the costal edge. In the Noctuoidea, the
metathorax is modified with a pair of tympanal organs. There are a
variety of wing coupling mechanisms that connect the forewings and
the hindwings. The more primitive groups have an enlarged lobe,
jugum, at the base of the forewing that folds under the hindwing in
flight. Other groups have a frenulum on the hindwing that hooks
under a retinaculum on the forewing. In some groups such as the
Psychidae, Lymantriidae, the females are flightless and have
reduced wings.

The abdominal segments 7-10 or 8-10 are modified to form the
external genitalia. The abdomen is connected to the thorax in the
more recent families by muscles connectd to projections from the
abdominal sternite 2. Paired hearing organs at the base of the
abdomen occur in the Pyraloidea and Geometroidea. Males have
glandular organs such as expandable hair brushes or tufts, or as
thin-walled, eversible sacs (coremata), from the intersegmental
membranes. The genitalia are complex and provide the basis for
species discrimination in most families and also in family
identification.

Primitive groups have a single genital aperture near the end of the
abdomen through which both copulation and egg laying occur. This
character is used to designate the Monotrysia. Hepialidae and
related families have an external groove that carries sperm from
the copulatory opening (gonopore) to the (ovipore) and are termed
exoporian. The remaining groups have an internal duct that carry
sperm and form the Ditrysia, with two distinct openings each for
copulation and egg-laying.

Families

There are about 69 families in this order with variations depending
on the taxonomic treatment (see the family template box at the
bottom of this section).

The Lepidoptera are divided into several suborders, the largest
being Glossata, the vast majority of which
are Ditrysia.

Several other classifications of lepidopteran families are used in
older literature. These include the Rhopalocera (club-horned) consisting of what are
commonly called butterflies and the Heterocera (varied-horned) consisting of the
moths. However, Rhophalocera is a natural (monophyletic) group, while Heterocera is a
paraphyletic assemblage.

Another non-standard classification separates the Lepidoptera into
Microlepidoptera for the smaller
species (mostly moths) and Macrolepidoptera for the larger
species.

Among the first entomologists to study fossil insects and their
evolution was Samuel Hubbard
Scudder (1837-1911), who worked on butterflies. He published a
study of the Florissant deposits of Colorado. Andreas V.Martynov (1879-1938) recognized the
close relationship between Lepidoptera and Trichoptera in his
studies on phylogeny. Lepidoptera tend not to be as common as some
other insects in the habitats that are most conducive to
fossilization, such as lakes and ponds, and their juvenile stage
has only the head capsule as a hard part that might be preserved.
Yet there are fossils, some preserved in amber and some in very
fine sediments. Leaf mines are also seen
in fossil leaves, although the interpretation of them is tricky.
The earliest fossil is Archaeolepis mane from the Jurassic,
about 190 million years ago in Dorset, UK. It consists of wings and
shows scales with parallel grooves under a scanning electron
microscope and the characteristic wing venation pattern shared with
Trichoptera. Only 2 more sets of
Jurassic Lepidopteran fossils have been found, and 13 sets in the
Cretaceous. From there, many more fossils are found from the
Tertiary, and particularly the Eocene Baltic amber.

Major contributions in the 20th century included the creation of
the monotrysia and ditrysia (based on female genital structure) by
Borner in 1925 and 1939. Willi Hennig
(1913-1976) developed the cladistic
methodology and applied it to insect phylogeny. Niels P.
Kristensen, E. S. Nielsen and D. R. Davis studied the relationships
among monotrysian families and Kristensen
worked more generally on insect phylogeny
and higher Lepidoptera too.. While it is often found that DNA-based
phylogenies differ from those based on morphology, this has not been the case
for the Lepidoptera; DNA phylogenies correspond to a large extent
to morphology-based phylogenies.

Many attempts have been made to group the superfamilies of the
Lepidoptera into natural groups, most of which fail because one of
the two groups is not monophyletic:
Microlepidotera and Macrolepidoptera, Heterocera and Rhopalocera,
Jugatae and Frenatae, Monotrysia and Ditrysia.

Phylogeny

A proposed phylogeny of the principal lepidopteran
groups.

It has long been noted that the Lepidoptera and the Trichoptera (caddisflies) share many
similarities that are lacking in other insect orders. Among these
are:

females, rather than males, are heterogametic (i.e. their sex
chromosomes differ)

Thus the two sister orders are grouped into the Amphiesmenoptera. The group probably
evolved in the Jurassic, diverging from the
extinct Necrotaulidae. Lepidoptera differ from the Trichoptera in several features, including wing
venation, form of the scales on the wings, loss of the cerci, loss of an ocellus, and
changes to the legs.

The oldest, most basal lineages of
Lepidoptera have as adults, not the curled tongue or proboscis characteristic of most members of the
order, but chewing mandibles (Micropterigidae, Agathiphagidae and Heterobathmiidae). Micropterigidae larvae
feed on decaying leaves (much like the Trichoptera), fungi,
liverworts or live leaves. The adults chew
pollen or spores of ferns. In the Agathiphagidae, larvae feed
inside seeds of kauri pines, and in
Heterobathmiidae the larvae mine leaves of Nothofagus, the southern beech. These
families also have mandibles in the pupal stage, which help the
pupa emerge from the seed or cocoon just before adult
emergence.

The Eriocraniidae have a short coiled
proboscis in the adult stage, and retain mandibles for the purpose
of escaping the cocoon, but they are non-functional thereafter.
They, and most of the other non-ditrysian families, are primarily
leaf miners in the larval stage. In
addition to the proboscis, there is a change in the scales among
these basal lineages, with later lineages showing more complex
perforated scales.

With the evolution of the Ditrysia in the
mid-Cretaceous, there was a major
reproductive change. The Ditrysia, which comprise 98% of the
Lepidoptera, have two separate openings for reproduction in the
females (as well as a third opening for excretion), one for mating,
and one for laying eggs. The two are linked internally by a seminal
duct. (In more basal lineages there is one cloaca, or later, two openings and an external sperm
canal.) Of the early lineages of Ditrysia, Gracillarioidea and Gelechioidea are mostly leaf miners, but more
recent lineages feed externally. In the Tineoidea, most species feed on plant and animal
detritus and fungi, and build shelters in the larval stage.

The Yponomeutoidea is the first group
to have significant numbers of species whose larvae feed on
herbaceous plants, as opposed to woody plants. They evolved about
the time that flowering plants underwent an expansive adaptive radiation in the mid-Cretaceous, and the Gelechioidea that evolved at
this time also have great diversity. Whether the processes involved
co-evolution or sequential evolution,
the diversity of the Lepidoptera and the angiosperms increased
together.

In the so-called "macrolepidoptera", which constitutes about
60% of Lepidopteran species, there was a general increase in size,
better flying ability (via changes in wing shape and linkage of the
forewings and hindwings), reduction in the adult mandibles, and a
change in the arrangement of the crochets (hooks) on the larval
prolegs, perhaps to improve the grip on the host plant. Many also
have tympanal organs, that allow them
to hear. These organs evolved eight times, at least, because they
occur on different body parts and have structural differences.The
main lineages in the macrolepidoptera are the Noctuoidea, Bombycoidea, Lasiocampidae, Mimallonoidea, Geometroidea and Rhopalocera. Bombycoidea plus Lasiocampidae plus
Mimallonoidea may be a monophyletic
group. The Rhopalocera, comprising the Papilionoidea (Butterflies), Hesperioidea (skippers), and the Hedyloidea (moth-butterflies), are the most
recently evolved. There is quite a good fossil record for this
group, with the oldest skipper about 56 million years old.

Dugdale, JS, 1996. Natural history and identification of
litter-feeding Lepidoptera larvae (Insecta) in beech forests,
Orongorongo Valley, New Zealand, with especial reference to the
diet of mice (Mus musculus). Journal of The Royal Society
of New Zealand, Volume 26, Number 2, pp 251-274